Concentrations of Credit Risk - Residential Real Estate Loans by Geographic Region (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Concentration Risk [Line Items]
Total Loans	$ 41,948.3	$ 43,390.6
Personal
Concentration Risk [Line Items]
Total Loans	21,517.3	23,111.8
Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	6,077.3	6,109.9
Florida | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	1,597.9	1,636.5
California | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	1,291.7	1,371.9
Illinois | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	548.5	591.3
New York | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	539.3	510.8
Colorado | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	337.7	309.9
Texas | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	301.4	308.7
All other | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	$ 1,460.8	$ 1,380.8